Testicles are more often used as such a sign. You know mistletoe and the whole druid tradition that together with a bit of nordicness, became the kiss tradition thingie? Misteltoes seed looks like semen. Semen, balls and love.

Actually it's a mystery. Could also be from the Silphium seed, a seed so treasured said to be worth its weight in gold. Now extinct because the Romans used it all up for boning. (believed to have been natural contraceptive)